Yakima Ridge is a long anticline mountain ridge in Yakima County and Benton County in the U.S. state of Washington . From its western end just north of the city of Yakima , the ridge runs east-southeast through the Yakima Training Center to its eastern end at Hanford Reach National Monument and the Hanford Site . Yakima Ridge is paralleled on the north by Umtanum Ridge and on the south by the Rattlesnake Hills . Moxee Valley and Black Rock Valley lie south of Yakima Ridge.
25-455: Yakima Ridge is part of the Yakima Fold Belt of east-tending long ridges formed by the folding of Miocene Columbia River basalt flows . The Yakima River cut a water gap through Yakima Ridge at Selah Gap . The river cut through other ridges at locations including Umtanum Ridge Water Gap and Union Gap at Ahtanum Ridge. This Benton County, Washington state location article
50-480: A ramp and typically forms at an angle of about 15°–30° to the bedding. Continued displacement on a thrust over a ramp produces a characteristic fold geometry known as a ramp anticline or, more generally, as a fault-bend fold . Fault-propagation folds form at the tip of a thrust fault where propagation along the decollement has ceased, but displacement on the thrust behind the fault tip continues. The formation of an asymmetric anticline-syncline fold pair accommodates
75-402: A sedimentary sequence, such as mudstones or halite layers; these parts of the thrust are called decollements . If the effectiveness of the decollement becomes reduced, the thrust will tend to cut up the section to a higher stratigraphic level until it reaches another effective decollement where it can continue as bedding parallel flat. The part of the thrust linking the two flats is known as
100-408: A sedimentary sequence, such as the top and base of a relatively strong sandstone layer bounded by two relatively weak mudstone layers. When a thrust that has propagated along the lower detachment, known as the floor thrust , cuts up to the upper detachment, known as the roof thrust , it forms a ramp within the stronger layer. With continued displacement on the thrust, higher stresses are developed in
125-498: A series of generally east-trending narrow asymmetrical anticlinal ridges and broad synclinal valleys formed by folding of Miocene Columbia River basalt flows and sediments. In most parts of the belt the folds have a north vergence (Columbia Hills' south vergence is an exception) with the steep limb typically faulted by imbricate thrust faults . Fold lengths range from 1 km to 100 km with wavelengths from several kilometers to 20 km. A graben underlies nearly
150-513: Is a stub . You can help Misplaced Pages by expanding it . This Yakima County, Washington state location article is a stub . You can help Misplaced Pages by expanding it . Yakima Fold Belt The Yakima Fold Belt of south-central Washington , also called the Yakima fold-and-thrust belt , is an area of topographical folds (or wrinkles) raised by tectonic compression. It is a 14,000 km (5,400 sq mi) structural-tectonic sub province of
175-737: Is also located on, and the orientation and spacing of some of the Folds influenced by, the Olympic–Wallowa Lineament (OWL), a broad zone of linear topographical features (dashed yellow line) extending from the Olympic Peninsula in northwestern Washington to the Wallowa Mountains in northeastern Oregon. It is the central portion of the Olympic–Wallowa Lineament , referred to as the Cle Elum-Wallula deformed zone (CLEW), constising of
200-416: Is typically a lozenge-shaped duplex. Most duplexes have only small displacements on the bounding faults between the horses, which dip away from the foreland. Occasionally, the displacement on the individual horses is more significant, such that each horse lies more or less vertically above the other; this is known as an antiformal stack or imbricate stack . If the individual displacements are still greater,
225-601: The Alps , and the Appalachians are prominent examples of compressional orogenies with numerous overthrust faults. Thrust faults occur in the foreland basin , marginal to orogenic belts. Here, compression does not result in appreciable mountain building, which is mostly accommodated by folding and stacking of thrusts. Instead, thrust faults generally cause a thickening of the stratigraphic section . When thrusts are developed in orogens formed in previously rifted margins, inversion of
250-692: The Potholes Reservoir , another (Saddle Mountains) terminates just south of there, near the town of Othello (red circle). South of the Tri-Cities the rampart of the Horse Heaven Hills extends for a short distance past the Columbia River. The ends of these ridges mark the edge of a block of continental crust (part of the North American craton , indicated by the dashed orange line) that has resisted
275-412: The ocean trench margin of subduction zones, where oceanic sediments are scraped off the subducted plate and accumulate. Here, the accretionary wedge must thicken by up to 200%, and this is achieved by stacking thrust fault upon thrust fault in a melange of disrupted rock, often with chaotic folding. Here, ramp flat geometries are not usually observed because the compressional force is at a steep angle to
SECTION 10
#1733084723827300-626: The Washington Pacific coast about 7 millimeters per year. Studies of the motion of the Yakima Fold Belt have been undertaken to evaluate seismic hazards at the Hanford Site . Thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If
325-417: The angle of the fault plane is lower (often less than 15 degrees from the horizontal ) and the displacement of the overlying block is large (often in the kilometer range) the fault is called an overthrust or overthrust fault . Erosion can remove part of the overlying block, creating a fenster (or window ) – when the underlying block is exposed only in a relatively small area. When erosion removes most of
350-514: The buried paleo-rifts can induce the nucleation of thrust ramps. Foreland basin thrusts also usually observe the ramp-flat geometry, with thrusts propagating within units at very low angle "flats" (at 1–5 degrees) and then moving up-section in steeper ramps (at 5–20 degrees) where they offset stratigraphic units. Thrusts have also been detected in cratonic settings, where "far-foreland" deformation has advanced into intracontinental areas. Thrusts and duplexes are also found in accretionary wedges in
375-446: The continuing displacement. As displacement continues, the thrust tip starts to propagate along the axis of the syncline. Such structures are also known as tip-line folds . Eventually, the propagating thrust tip may reach another effective decollement layer, and a composite fold structure will develop with fault-bending and fault-propagation folds' characteristics. Duplexes occur where two decollement levels are close to each other within
400-557: The entire Yakima Fold Belt and has been subsiding since Eocene time, and continues to sink at a slow rate. A 2011 report found aeromagnetic , gravity , and paleoseismic evidence that the Yakima Fold Belt is linked to active Puget Sound faults . Geodetic studies of the Oregon Rotation show that Oregon is rotating about a point somewhat south of Lewiston, Idaho compressing the Yakima fold an average of 3 millimeters per year, and
425-429: The footwall of the ramp due to the bend on the fault. This may cause renewed propagation along the floor thrust until it again cuts up to join the roof thrust. Further displacement then takes place via the newly created ramp. This process may repeat many times, forming a series of fault-bounded thrust slices known as imbricates or horses , each with the geometry of a fault-bend fold of small displacement. The final result
450-505: The horses have a foreland dip. Duplexing is a very efficient mechanism of accommodating the shortening of the crust by thickening the section rather than by folding and deformation. Large overthrust faults occur in areas that have undergone great compressional forces. These conditions exist in the orogenic belts that result from either two continental tectonic collisions or from subduction zone accretion. The resultant compressional forces produce mountain ranges. The Himalayas ,
475-469: The overlying block, leaving island-like remnants resting on the lower block, the remnants are called klippen (singular klippe ). If the fault plane terminates before it reaches the Earth's surface, it is called a blind thrust fault. Because of the lack of surface evidence, blind thrust faults are difficult to detect until rupture. The destructive 1994 earthquake in Northridge, Los Angeles, California ,
500-847: The sedimentary layering. Thrust faults were unrecognised until the work of Arnold Escher von der Linth , Albert Heim and Marcel Alexandre Bertrand in the Alps working on the Glarus Thrust ; Charles Lapworth , Ben Peach and John Horne working on parts of the Moine Thrust in the Scottish Highlands ; Alfred Elis Törnebohm in the Scandinavian Caledonides and R. G. McConnell in the Canadian Rockies. The realisation that older strata could, via faulting, be found above younger strata
525-653: The shaded-relief image) is due to their formation in a layer of lava flows and sedimentary deposits that have filled-in and generally smoothed the topographic surface of a large area of the Columbia Basin . The extent of these lava flows was limited to the west and north by the rising Cascade Mountains and the Wenatchee Mountains . The lava flows extend east well beyond this image, but the Yakima Folds do not. The northernmost fold seen here (Frenchman Hills) ends at
SECTION 20
#1733084723827550-740: The tectonic compression that formed the ridges. The southernmost ridge of the Yakima Fold Belt is the Columbia Hills on the north side of the Columbia River. The pattern of folding continues with the Dalles-Umatilla Syncline just south of the Columbia River, and further into Oregon with the Blue Mountains anticline, which approximately parallels the Klamath-Blue Mountain Lineament that marks the southeastern edge of Siletzia (see geological map, below). The Yakima Fold Belt
575-587: The western Columbia Plateau Province resulting from complex and poorly understood regional tectonics. The folds are associated with geological faults whose seismic risk is of particular concern to the nuclear facilities at the Hanford Nuclear Reservation (immediately northwest of the Tri-Cities) and major dams on the Columbia and Snake Rivers . The topographical distinctness of the Yakima Folds (see
600-439: Was arrived at more or less independently by geologists in all these areas during the 1880s. Geikie in 1884 coined the term thrust-plane to describe this special set of faults. He wrote: By a system of reversed faults, a group of strata is made to cover a great breadth of ground and actually to overlie higher members of the same series. The most extraordinary dislocations, however, are those to which for distinction we have given
625-456: Was caused by a previously undiscovered blind thrust fault. Because of their low dip , thrusts are also difficult to appreciate in mapping, where lithological offsets are generally subtle and stratigraphic repetition is difficult to detect, especially in peneplain areas. Thrust faults, particularly those involved in thin-skinned style of deformation, have a so-called ramp-flat geometry. Thrusts mainly propagate along zones of weakness within
#826173